it depends on what you are launching, how you are launching it, and the people you are sharing the project with.
Do you intend to do a private launch to keep the idea from spreading beyond certain boundaries? If so, you'll want to draft a non-disclosure agreement between all parties involved. If not, no worries here.
Do you intend to solicit investment? If so, you'll want to form a business entity (typically a corporation or a LLC) and draft shareholders/membership contracts. Actually, if you plan to accept online payments through a payment gateway, you typically need company verification documents in order to open a merchant account.
Do you intend to hire employees? If so, you'll need to draft employment contracts and think compensation.
I'd personally register a corporation and start marketing the product with a memorable name (that isn't taken in your field, of course).
No, you don't have to spend thousands of dollars to hire a lawyer. Many of these things you can do yourself. Check out these DIY kits: Here
Nolo also has some good DIY guides.
Disclaimer: This is not legal advice and does not constitute an attorney-client relationship.